A silicon wafer is widely used as a substrate for a semiconductor device.
Generally, among a series of processes to manufacture the silicon wafer, there is an ingot slicing process to slice an ingot grown with a given length by a growing process into plural pieces of single crystal silicon wafers.
There are various type methods for the ingot slicing process. Representative ingot slicing methods may include an ODS (Outer Diameter Saw) method to slice a single crystal ingot using diamond particles fixed to an outer diameter region of a thin film, an IDS (Inner Diameter Saw) method to slice a single crystal ingot using diamond particles fixed to an inner diameter region of a doughnut-shape thin film, and a WS (Wire Saw) method to slice an single crystal ingot using frictions generated between the ingot and an abrasive slurry applied to wires such as piano wires having high tensile strength while a slurry solution is being sprayed onto running wires. Among these methods, the wire saw method forms plural pieces of single crystal silicon wafers at the same time, thus being widely employed and increasing yield rates of the wafers per unit time.
FIG. 1 is a perspective view of a conventional wire saw apparatus.
The conventional wire saw apparatus, as shown in FIG. 1, includes a mounting block 110 to fix an ingot 112 using a beam 114 therebetween, wire guides 120 disposed under the ingot 112, around outer faces of which wires 122 are wound with a regular interval or pitch, and slurry supply nozzles 130 to supply a slurry 132 to the wires 122.
One surface of the beam 114 is adhered to the mounting block 110 using an organic bonding material such as epoxy therebetween. The other surface of the beam 114 is adhered to the ingot 112 using another organic bonding material therebetween. Next, by curing the two organic bonding materials, the mounting block 110, beam 114 and ingot 112 are adhered to one another.
While the mounting block 110 and thus the ingot 112 fixed thereto are loaded to the wire saw apparatus, the ingot 112 begins to be sliced.
The wires 122 are wound around the outer faces of the wire guides 120 disposed under the ingot 112 with a regular pitch. The pitch between the wires 122 may determine the number and thickness of resulting sliced wafers.
The slurry supply nozzles 130 are disposed above the wires 122 to supply the slurry 132, which contains abrasive grains, thereto. Therefore, when the ingot 112 fixed to the mounting block 110 moves and comes into pressure contact with the running wires 112, the ingot 112 is sliced by the abrasive grains applied to the running wires 112.
However, the conventional wire saw apparatus has the following downsides.
FIG. 2 is an enlarged view of the wire guide 120 of the conventional wire saw apparatus. FIG. 3 illustrates cut traces formed when slicing the ingot using the conventional wire saw apparatus.
The wire guide may be stretched or expanded by heat generated from the conventional wire saw apparatus when slicing the ingot 112. Referring to FIG. 2, the wire guide 120 may be stretched in a direction from a first proximal end 120a proximal to a support 126 to support the wire guide 120 to a second distal end 120b distant from the support 126.
Accordingly, as seen from the cut traces A to C shown in FIG. 3, as the sliced faces of the ingot 112 are located more closely to the second end 120b, the corresponding curvatures of the sliced faces, in particular, those of initially-cut portions of the sliced faces, become larger. As a result, nano-topography of a polished wafer is deteriorated.
In other words, at an initial time, the ingot 112 fixed to the mounting block 110 comes into pressure contact with the wire guide 120 around which the wires 122 are wound in a state in which the wire guide is not stretched. However, at later time, the ingot 112 comes into pressure contact with the wire guide 120 in a state where the wire guide is stretched toward the second end 120b side due to heat generated when the ingot 112 is being sliced while coming into pressure contact with the wire guide 120. Therefore, curvature of a cut trace C of the ingot 112 at the second end 102b side becomes larger.
Accordingly, there is a need to improve wafer quality by controlling expansion or stretching of the wire guide 120 so as to prevent the sliced faces of the ingot 112 from being curved.